Glacier Produce Oilless Bush : Plastic Bonded to Metal
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THE development of a bearing bush
that will function satisfactorily without need for a lubricant has been a possibility for many years, and although there have been types for use under light load condition, it has been left to the plastic industry to provide the basic material for a general-purpose bearing.
The plastic used is polytetrafluoroethylene (ptfe). It is extremely inert and possesses an unusually low dry coefficient of friction. Its use in the solid form as a bearing material is limited by its poor thermal conductivity, poor temperature stability, high coefficient of thermal expansion, cold flow under light loads, and an elastic memory or tendency to change shape without any externally applied forces.
These disadvantages have been overcome by using an impregnated bimetal material. Wrapped bushes of this type were introduced last week by the Glacier Metal Co., Ltd., Alperton, Wembley, Middx., who are initially making available a limited range of 38 sizes, and 18 sizes of thrust washer, The Glacier dry bearing consists of a steel backing lined, in strip form, with porous bronze impregnated with ptfe substantially to the full depth of the porous bronze layer, leaving a surface layer in the form of a complete film about 0.001 in. thick.
In a normal bearing, the oil serves to dissipate the heat generated and so facilitates its rapid removal from the bearing surface. In a dry bearing no liquid is present, and so the load and speed capacity of the bearing are determined largely by the ability of the assembly to dissipate heat.
In the case of the Glacier dry bearing, a pressure velocity factor-load in p.s.i. of the projected area multiplied by the surface velocity in ft. per min.-is quoted. The following table gives some of the conditions under which this type of bearing and thrust washer has given satisfactory service: In all the cases given, a soft mild-steel mating surface was used and when the tests were ended there was no sign of a breakdown of The bearing surface.
It is not possible at this stage in development to specify all the suitable applications for the bearings or thrust washers, but there are numerous locations in a commercial-vehicle chassis where the use of a bearing which did Got call for periodical lubrication would do much to reduce maintenance.